The discussions of church fathers of some of textual differences shows that most of the important differences have been talked about over the last sixteen or seventeen centuries. It also shows that the existence of such differences was never a reason to give up trust in the Scriptures.

https://www.desiringgod.org/articles/how-we-got-the-bible

The sixteenth- and seventeenth-century Reformed churches produced several families of orthodox confessions that promoted the Calvinist faith and differentiated it from Roman Catholicism and other groups of Protestant churches. The most well-known of these groups of confessions were the Swiss-Hungarian family, represented by the First and Second Helvetic Confessions (1536 and 1566) and the Helvetic Consensus Formula (1675); the Scottish-English family, represented by the Scots Confession (1560), the Thirty-nine Articles (1563), the Westminster Confession of Faith (1647), and the Shorter (1648) and Larger (1648) Catechisms of the Westminster Assembly; and the Dutch-German family, represented by the Three Forms of Unity: the Belgic Confession of Faith (1561), the Heidelberg Catechism (1563), and the Canons of Dort (1618-1619). Of those Reformed confessions, the seven most diligently adhered to by various Reformed denominations today are the Three Forms of Unity, the Second Helvetic Confession, and the Westminster Confession and Catechisms. They can be called “living” doctrinal standards because they are sanctioned officially by numerous twenty-first century Reformed churches. . .

One cannot avoid being amazed at the remarkable unity of Calvinist theology in the sixteenth and seventeenth centuries.

Joel R. Beeke, Living for God’s Glory: An Introduction to Calvinism , Loc. 384,498.

One of the striking features of early Calvinists was their dedication to making confessional statements. Those Calvinists and subsequent Reformed believers held that confessions have only a provisional character, since they reflect the limited insights of mere men. Their authority is derived and must always be subordinated to Scripture, which possesses intrinsic authority. Nevertheless, they recognized that confessions make a valuable contribution to the church’s primary tasks: worshiping (the doxological task), witnessing (the declarative task), teaching (the didactic task), and defending the faith (the disciplining task). Reformed confessions have been particularly effective in helping the church unitedly declare what it believes, what it is to be, and how it is to be an evangelical testimony to those outside of its fellowship.

Joel E. Beeke, Living for God’s Glory: An Introduction to Calvinism, Loc. 376.

Q. 74. What is adoption?

A. Adoption is an act of the free grace of God, in and for his only Son Jesus Christ, whereby all those that are justified are received into the number of his children, have his name put upon them, the Spirit of his Son given to them, are under his fatherly care and dispensations, admitted to all the liberties and privileges of the sons of God, made heirs of all the promises, and fellow-heirs with Christ in glory.

Westminster Larger Catechism

Q. 34. What is adoption?

A. Adoption is an act of God’s free grace, whereby we are received into the number, and have a right to all the privileges, of the sons of God.

Westminster Shorter Catechism

God is good. He is a beneficial sovereign. He has established institutions among men for the good of man; and committed their administration to the hands of men. So far as they come up to the standard, these institutions, in their actual operation, exercise a salutary influence over all who subject themselves to their sway and direction. But God is also just — a righteous law-giver. The divine government gives no countenance to sin: it is ever against it. And, hence, the Most High has invested all his institutions with some kind and degree of restraining power; and has given them laws by which they are to be guided in the disciplinary or punitive department of their functions.

James M. Wilson, Civil Government: An Exposition on Romans XIII. 1-7 (Philadelphia: William S. Young, 1853), 69-70.

Under [J. A.] Turretin’s guidance, the Council of Geneva tellingly ruled that candidates for ordination need not subscribe to the Formula or even to the Canons of Dordt, but only to the Bible and Calvin’s Catechism, in order to facilitate union among the Reformed, Anglican, and Lutheran churches. Though the younger Turretin aimed at an enlightened, moderate orthodoxy that would defeat philosophical challenges to Christianity and unite Protestantism, his efforts actually opened the gates for heterodoxy to enter into the citadel of Calvinism.

Joel R. Beeke, Debated Issues in Sovereign Predestination: Early Lutheran Predestination, Calvinian Reprobation, and Variations in Genevan Lapsarianism, 211.

The abolition of requirements for subscription to confessional statements in the name of toleration opened the door for apostasy from essential Reformed doctrines. A watershed moment took place in Genevan theology when J. A. Turretin successfully abolished the requirement that candidates for the ministry subscribe to confessional standards; they needed merely to pledge fidelity to the Bible. Such vague commitments could not wall out heresy, heterodoxy, and apostasy.

Joel R. Beeke, Debated Issues in Sovereign Predestination: Early Lutheran Predestination, Calvinian Reprobation, and Variations in Genevan Lapsarianism, 222.

As an advocate of natural theology, J. A. Turretin had no interest in the decrees of God. He taught that the doctrine of predestination had only led to “wild excess” in Protestant circles. . . . For J. A. Turretin, the notion of sin and man’s unworthiness of salvation did not bear any implications for the divine decree. His Fundamentals in Religion reveal how completely he had depart from his father’s theology in many cardinal doctrines of Reformed orthodoxy. His fight to abrogate the [Genevan] Formula Consensus of 1675, which he accomplished by 1706, spelled the final defeat for Reformed orthodoxy at Geneva Academy.

Joel R. Beeke, Debated Issues in Sovereign Predestination: Early Lutheran Predestination, Calvinian Reprobation, and Variations in Genevan Lapsarianism, 210.

Around 1750 Reformed theology everywhere fell into decay. The elements responsible for this decomposition, already present in the previous century, continued to have their effect, undermining dogmatics. After Cocceianism in the Netherlands had emerged victorious came the Ear of Toleration (1740–70). The power of truth was denied; people retreated from the church’s confessions to Scripture and abandoned doctrines characteristic for the Reformed faith, such as original sin, the covenant of works, limited atonement, etc. In beautiful dress and the name of being biblical, a variety of Remonstrant and Socinian errors rose to the surface. At best, those who professed the Reformed religion accepted the theology that they had “in stock,” but they no longer had their hearts in it, nor did they any longer speak out of its content. The old dogmatics [simply] became an object of historical study.

Herman Bavinck, Reformed Dogmatics: Prolegomena, I:189.

In time, the Reformed movement developed into two very similar systems of theology: the Continental Reformed, represented primarily in the Netherlands by its Three Forms of Unity-the Belgic Confession, Heidelberg Catechism, and Canons of Dort; and British-American Presbyterianism, expressed in the Westminster standards-the Westminster Confession of Faith, the Larger Catechism, and the Shorter Catechism. These two systems were not opposed to or entirely separate from each other, however. For example, British Puritans profoundly influenced the Dutch Further Reformation in the seventeenth century. Likewise, the Italian-Swiss Francis Turretin (1623-1687) profoundly affected American Presbyterianism. Turretin’s systematic theology was taught at Princeton Seminary until the 1870s, when it was replaced by that of Charles Hodge.

Both systems of Reformed theology parted ways with Lutheranism. By the end of the sixteenth century, Calvinism differed from Lutheranism in the following areas:

• Approach to the Lord’s Supper. Lutherans maintained the doctrine of consubstantiation, which holds that Christ is physically present in, with, and under the elements in the Lord’s Supper. They resisted any attempt to explain Jesus’ statement “this is my body” as a metaphor, saying that such efforts opened the door to allegorizing away the gospel itself. Furthermore, they said, if all that is offered in Communion is a spiritual Christ, the sacrament presents a truncated gospel that offers no comfort to believers whose bodies eventually will die. Lutherans would be satisfied only with a concrete, historical Christ. The Reformed leaders said that the incarnate, historical Christ is now risen and ascended, and therefore is not present in the Supper in the way He was prior to His ascension. Furthermore, the concept of Christ’s spiritual presence does not mean something less than complete; rather, it refers to His ongoing work through His Spirit. The Reformed believed they were affirming all that the Lutherans wanted to protect, but in a clearer, more biblical manner.

• The primary function of the law. Luther generally regarded the law as something thing negative and closely allied with sin, death, or the Devil. He believed that the dominant function of the law is to abase the sinner by convicting him of sin and driving him to Christ for deliverance. Calvin regarded the law more as a guide for the believer, a tool to encourage him to cling to God and to obey Him more fervently. The believer must try to follow God’s law not as an act of compulsory duty, but as a response of grateful obedience. With the help of the Spirit, the law provides a way for a believer to express his gratitude.

• Approach to salvation. Both Lutherans and Calvinists answered the question tion “What must I do to be saved?” by saying that Spirit-worked repentance toward God and faith in the Lord Jesus Christ and His substitutionary work of atonement are necessary. But Lutherans had a tendency to remain focused on the doctrine of justification, whereas Calvinists, without minimizing justification, pressed more than Lutherans toward sanctification, which asks, “Having been justified by God’s grace, how shall I live to the glory of God?” Calvinism thus became more comprehensive than Lutheranism in explaining how salvation works itself out in the life of a believer.

• Understanding of predestination. In the late sixteenth century, most Lutherans moved away from Luther and the Calvinists, who asserted the predestination of both the elect and the reprobate rather than the predestination of the elect only. Reformed theologians believed this shift in thinking was at odds with the content of Romans 9 and similar passages, as well as with the comprehensive sovereignty of God. The Calvinists were convinced that election is sovereign and gracious, and that reprobation is sovereign and just. No one who enters heaven deserves to be there; no one who enters hell deserves anything different. As Calvin said, “The praise of salvation is claimed for God, whereas the blame of perdition is thrown upon those who of their own accord bring it upon themselves.”

• Understanding of worship. Luther’s reform was more moderate than Calvin’s, retaining more medieval liturgy. Following their leaders, the Lutherans and Calvinists differed in their views of how Scripture regulates worship. The Lutherans taught that we may include in worship what is not forbidden in Scripture; the Calvinists maintained that we may not include in worship what the New Testament does not command.

Joel R. Beeke, Living for God’s Glory: An Introduction to Calvinism, Loc. 235.